Research On Power Regulation Of Paralleled Inverters Using Virtual Impedance In Low-Voltage Microgrid

Microgrid is an important way to absorb distributed power,reducing the phenomenon of abandoning wind and solar energy,and improving the utilization of new energy.The droop control strategy is an important method for microgrid to control inverters.The control method without interconnected communication line has the advantage of "plug and play" and can realize flexible expansion of microgrid.However,affected by factors such as line impedance,the output power of parallel inverters in a low-voltage microgrid cannot be distributed in proportion to the droop coefficient.On basis of droop control strategy and virtual impedance method,this paper intensively studies the power distribution problem of low-voltage microgrid wireless parallel invertersBecause the line impedance of the low-voltage microgrid is resistive,unlike the traditional inductive transmission lines of the high voltage grid system,the traditional inductive droop control method is not applicable.In order to adapt to the resistive characteristics of the low-voltage lines,this paper adopts a resistive droop control strategy to achieve power decoupling.Meanwhile,virtual negative inductance is adopted to change the equivalent output impedance of the inverter as resistive,so that it can achieve better power decoupling control.The position of each distributed generation in the microgrid is random,and the feeder line impedance different,which makes the output active power of inverters based on resistive droop control unable to be reasonably distributed as required,which will lead to some problems such as overload of the distributed generation and over-discharged of the battery.Therefore,this paper proposes an adaptive virtual resistance control method based on local information,which can reduce the unsharing of the parallel inverters' output active power.This control method does not require communication between the inverters and the central controller,and only uses the active power and voltage values from the local inverter to compensate.It can coordinate the relationship between the power sharing accuracy and the voltage drop.The signal stability analysis is used to provide a basis for the value of virtual resistance coefficient.In order to verify the effectiveness of the proposed control method,a microgrid simulation model was built in Matlab/Simulink to compare with the existing control strategies.At the same time,an experimental system based on the RTDS experimental platform and DSP controller is used to conduct experimental verification.The results show that the control method can significantly reduce the power deviation of the parallel inverters and ensure the voltage operation within the rated range.However,the droop control is a differential adjustment,and the adaptive virtual resistance will increase the voltage drop,which makes the operating frequency and voltage of the microgrid deviate from the rated value.In order to ensure the stable operation of the microgrid,the frequency and voltage stability control loops are added to the inverter control system.The control strategy is also carried out without communication,which can make the frequency return to the rated value and significantly reduce the voltage deviation.Finally,simulation verification was performed in Matlab/Simulink.